Diagnostic tests based on a binding event between members of an analyte-anti-analyte binding pair are widely used in medical, veterinary, agricultural and research applications. Typically, such methods are employed to detect the presence or amount or an analyte in a sample, and/or the rate of binding of the analyte to the anti-analyte. Typical analyte-anti-analyte pairs include complementary strands of nucleic acids, antigen-antibody pairs, and receptor-receptor binding agent, where the analyte can be either member of the pair, and the anti-analyte molecule, the opposite member.
Diagnostics methods of this type often employ a solid surface having immobilized anti-analyte molecules to which sample analyte molecules will bind specifically and with high affinity at a defined detection zone. In this type of assay, known as a solid-phase assay, the solid surface is exposed to the sample under conditions that promote analyte binding to immobilized anti-analyte molecules. The binding event can be detected directly, e.g., by a change in the mass, reflectivity, thickness, color or other characteristic indicative of a binding event. Where the analyte is pre-labeled, e.g., with a chromophore, or fluorescent or radiolabel, the binding event is detectable by the presence and/or amount of detectable label at the detection zone. Alternatively, the analyte can be labeled after it is bound at the detection zone, e.g., with a secondary, fluorescent-labeled anti-analyte antibody.
U.S. Pat. No. 5,804,453 discloses a method of determining the concentration of a substance in a sample solution, using a fiber optic having a reagent (capturing molecule) coated directly at its distal end to which the substance binds. The distal end is then immersed into the sample containing the analyte. Binding of the analyte to the reagent layer generates an interference pattern and is detected by a spectrometer.
U.S. Pat. No. 7,394,547 discloses a biosensor that a first optically transparent element is mechanical attached to an optic fiber tip with an air gap between them, and a second optical element as the interference layer with a thickness greater than 50 nm is then attached to the distal end of the first element. The biolayer is formed on the peripheral surface of the second optical element. An additional reflective surface layer with a thickness between 5-50 nm and a refractive index greater than 1.8 is coated between the interference layer and the first element. The principle of detecting an analyte in a sample based on the changes of spectral interference is described in this reference, which is incorporated herein by reference.
U.S. Pat. No. 7,319,525 discloses a different configuration that a section of an optic fiber is mechanically attached to a tip connector consisting of one or more optic fibers with an air gap between the proximal end of the optic fiber section and the tip connector. The interference layer and then the biolayer are built on the distal surface of the optical fiber section.
An air gap between coupling fibers has several disadvantages. One drawback is the reduction in coupling efficiency. Another problem is poor alignment. Practically, it is difficult to maintain the same exact air gap size for different pairs of sensors and instruments. In addition, air-fiber interface tends to causing higher reflection back to the spectrometer that can decrease the measurement signal-to-noise ratio.
Although prior art provides functionality in utilizing bio-sensors based upon thin-film interferometer, there exists a need for improvements in the performance of the interferometer.